The present invention relates to a head drum device for performing either or both of writing and reading of a signal to and from a magnetic tape and to a magnetic recording/playback apparatus, including the head drum device. More particularly, the present invention is directed to a head drum device having a three-layered structure in which an intermediate drum is rotatable, and also to a magnetic recording/playback apparatus including the head drum device.
In recent years, video tape recorders have come into widespread use as magnetic recording/playback apparatuses using magnetic tape as a recording medium. In video tape recorders, a helical scan method, in which recording or playback of a signal is performed by helically winding a magnetic tape around a head drum device, which is provided with a rotatable magnetic head on its circumference, is commonly used. The head drum device used in such video tape recorders is generally of two types: one having a two-layered structure including a fixed lower drum and a rotatable upper drum having a magnetic head; the other having a three-layered structure including a fixed lower drum, a rotatable intermediate drum having a magnetic head, and a fixed upper drum.
FIG. 1 illustrates an example of the configuration of a conventional three-layered head drum device.
FIG. 1 is a side view of a conventional head drum device 40 having a three-layered structure. The head drum device 40 includes a fixed lower drum 31, an intermediate drum 32 rotatable coaxially with the lower drum 31, and an upper drum 43 fixed coaxially with the intermediate drum 32. The lower drum 31 is provided with a lead 31a around its circumference for assisting the helically wound magnetic tape 2 to travel. A motor mechanism and associated parts for rotating and driving the intermediate drum 32 are contained within the lower drum 31. On the other hand, on the circumference of the intermediate drum 32, magnetic heads 32a for writing or reading a signal to and from the magnetic tape 2 are mounted. In practice, a plurality (two or four) of magnetic heads 32a is usually mounted. A rotary transformer or the like serving as a signal transmission path between the magnetic head 32a and an external device is accommodated within the upper drum 43.
While a recording or playback operation is performed on the magnetic tape 2 in such a head drum device 40, as shown in FIG. 1, the magnetic tape 2 is guided by the lead 31a and travels while being wound around the circumference of the head drum device 40 at a predetermined angle. At this time, the intermediate drum 32 is rotated and the magnetic head 32a scans the magnetic tape 2 at an angle, thus performing writing and reading of signals. The upper drum 43 also serves to prevent the traveling magnetic tape 2 from being displaced upwardly to cover the head drum device 40.
In the three-layered head drum device 40, as shown in FIG. 1, the axial length of the rotatable intermediate drum 32 is smaller than the width of the magnetic tape 2, and thereby the magnetic tape 2 is wound around three layers, that is, the lower drum 31, the intermediate drum 32, and the upper drum 43. In contrast, in a head drum device having a two-layered structure including a fixed lower drum and a rotatable upper drum, the axial length of the upper drum is substantially equal to the width of the magnetic tape 2. Such a two-layered head drum device may be provided with a tape guide above the upper drum to prevent the magnetic tape 2 from covering the upper drum, thus often having an apparent three-layered structure. However, the structure of this type also is called a two-layered structure here. On the other hand, the structure in which the axial length of the intermediate drum 32 is smaller than the width of the magnetic tape 2 is called a three-layered structure.
A specific example of the head drum device 40 having a three-layered structure is shown in Japanese Unexamined Patent Application Publication No. 10-340504 which discloses a head drum device with good contact characteristics between the magnetic tape 2 and the magnetic head 32a. In the head drum device 40, rotating the intermediate drum 32 at high speed while a recording or playback operation is performed causes air to be sucked in by the force of rotation to form an air film between the outer peripheral surface and the magnetic tape 2. This air film allows the magnetic tape 2 to travel smoothly. However, this air film tends to have a thickness distribution such that it is thicker at an entry side of the magnetic tape 2 and thinner at an exit side thereof. In such a case, the contact pressure between the magnetic tape 2 and the magnetic head 32a is not uniform, so that accurate writing and reading of a signal to and from the magnetic tape are prevented. On the other hand, in the above-mentioned publication, such a problem is solved by bonding a belt-like metallic thin film on the lower drum 31 on the side where the magnetic tape 2 exits to form a projection.
In the head drum device 40 having a three-layered structure, in the course of using a tape cassette that feeds the magnetic tape 2, for example, the magnetic tape 2 may be charged with static electricity, so that the magnetic tape 2 is attracted to the head drum device 40 and clings to it when this tape cassette is loaded. If the magnetic tape 2 travels in such a condition, a sufficient air film cannot be generated between the outer peripheral surface of the head drum device 40 and the magnetic tape 2, which may cause the magnetic tape 2 to be damaged. Particularly, in the head drum device 40 having a three-layered structure, as described above, since the axial length of the circumference of the rotatable intermediate drum 32 is small, a sufficient air film fails to be generated when the magnetic tape 2 travels. Accordingly, the magnetic tape 2 is prone to cling to the head drum device 40.
Therefore, the conventional head drum device 40 having a three-layered structure has prevented electrostatic charge by using a non-magnetic metal, such as an aluminum alloy or a copper alloy, as the material of the upper drum 43. Further, in the conventional head drum device 40 with a three-layered structure, the intermediate drum 32 has been formed in such a manner that its outside diameter is equal to that of the upper drum 43, and the friction resistance has been restricted by making the surface on which the magnetic tape 2 travels smooth. Also, in order to prevent the magnetic tape 2 from being damaged when it is in contact with the outer peripheral surface of the upper drum 43, the surface of the upper drum 43 has been manufactured using the metallic material mentioned above formed with a precision of xc2x12 xcexcm. However, since manufacture of the upper drum 43 described above requires expensive materials, processing, equipment, and so on, use of a synthetic resin material whose cost is relatively low has been discussed.
However, the upper drum 43 made of a synthetic resin has high resistance, so that static electricity is likely to be charged, and therefore the magnetic tape 2 is prone to cling to the upper drum. Further, the manufacturing precision of the surface dimensions is largely reduced in injection molding of synthetic resin material compared with that of metallic material. Accordingly, since further reduction of the outside diameter by machining is necessary in order to obtain a manufacturing precision falling within the range of xc2x12 xcexcm that is required when manufacturing the upper drum 43, it is impossible to reduce the manufacturing costs.
Furthermore, in a magnetic recording/playback apparatus including the head drum device 40, when any stains or dust are attached on the outer peripheral surface of the upper drum 43, the surface of the magnetic tape 2 may be damaged. Thus, actions such as mounting parts for removing such stains or dust, managing the manufacturing process so as to prevent such stains or dust from being attached, cleaning, and so on have been required during the manufacturing process. As a result, the manufacturing costs have increased due to the increased number of manufacturing processes, additional equipment, and material costs for chemical agents, such as alcohol, used for cleaning, which are necessary for such actions.
The present invention is provided in order to solve such problems, and an object of the present invention is to provide a head drum device having a reduced manufacturing cost for the upper drum.
Another object of the present invention is to provide a magnetic recording/playback apparatus provided with a head drum device having a reduced manufacturing cost for the upper drum.
In order to solve the problems described above, the present invention provides, in a head drum device for performing either or both of writing and reading of a signal to and from a magnetic tape, the head drum device is characterized by comprising: a fixed lower drum having a lead for helically guiding the magnetic tape; an intermediate drum having a magnetic head on its outer peripheral surface, which is rotated and supported coaxially with the lower drum and is formed in such a manner that the axial length of the outer peripheral surface is smaller than the width of the magnetic tape; and an upper drum made of a synthetic resin containing carbon, which is fixed and supported coaxially with the intermediate drum.
In such a head drum device, use of carbon-containing synthetic resin as the material of the upper drum can prevent the magnetic tape from clinging to the head drum device due to electrostatic charge. Also, setting the outside diameter of the upper drum smaller than that of the intermediate drum can eliminate the need for a high-level of manufacturing precision in the manufacture of the upper drum. Thus, it is possible to reduce the manufacturing cost for the upper drum.
Also, the present invention provides, in a magnetic recording/playback apparatus for performing either or both recording and playback of a signal on a magnetic tape, the magnetic recording/playback apparatus is characterized by having a head drum device comprising: a fixed lower drum having a lead for helically guiding the magnetic tape; an intermediate drum having a magnetic head on its outer peripheral surface, which is rotated and supported coaxially with the lower drum and is formed in such a manner that the axial length of the outer peripheral surface is smaller than the width of the magnetic tape; and an upper drum made of a synthetic resin containing carbon, which is fixed and supported coaxially with the intermediate drum.
In such a magnetic recording/playback apparatus, use of carbon-containing synthetic resin as the material of the upper drum of the head drum device can prevent the magnetic tape from clinging to the head drum device due to electrostatic charge. Also, setting the outside diameter of the upper drum smaller than that of the intermediate drum can eliminate the need for a high-level of manufacturing precision in the manufacture of the upper drum. Thus, it is possible to reduce the manufacturing cost for the upper drum.